Terrestrial magnetic sensor

Abstract

A terrestrial magnetic sensor has a bobbin body having a magnetic core inserting groove, a silicon gel filled in the magnetic core inserting groove, a magnetic core buried in the silicon gel filled in the magnetic core inserting groove, and a bobbin cover for closing the magnetic core inserting groove of the bobbin body. Thus, this terrestrial magnetic sensor can suppress the decrease in the magnetic permeability by burying a magnetic core in a silicon gel and can be hardly affected by the influences of the variations in an environmental temperature and an external stress.

What is claimed is: 
     
       1. A terrestrial magnetic sensor comprising: a bobbin body having a magnetic core inserting groove,   a silicon gel filled in the magnetic core inserting groove,   a magnetic core buried in the silicon gel filled in the magnetic core inserting groove, and   a bobbin cover for closing the magnetic core inserting groove of the bobbin body.   
     
     
       2. A terrestrial magnetic sensor according to claim 1, wherein said magnetic core is formed in a ring shape and composed of a Permalloy, and wherein said bobbin body and bobbin cover are correspondingly ring-shaped such that their combination defines a toroidal bobbin containing said magnetic core, said terrestrial magnetic sensor further comprising a coil wound in a toroidal shape about said toroidal bobbin. 
     
     
       3. A method for manufacturing a terrestrial magnetic sensor as claimed in claim 1 comprising the steps of: defining the shapes of the bobbin body and bobbin cover such that their combination results in a toroidal bobbin,   filling said magnetic core inserting groove of said bobbin body partially with said silicon gel,   then inserting said magnetic core into said partially filled magnetic core inserting groove,   then further filling said magnetic core inserting groove with said silicon gel such that said core is buried in said silicon gel,   engaging said bobbin cover to said bobbin body to cover said magnetic core inserting groove and form said toroidal bobbin, and   then winding a coil in a toroidal shape about the toroidal bobbin to form a toroidal coil.   
     
     
       4. A method for manufacturing a terrestrial magnetic sensor as claimed in claim 3, further comprising the steps of: inserting said toroidal coil into a holding case, leaving a gap between said toroidal coil and said holding case,   filling said gap with resin,   then drying the resin,   providing first and second windings about said holding case for detecting magnetism, the first and second windings being perpendicular to each other,   then bonding a printed substrate having terminals to said holding case, and   coupling wires of said toroidal coil and said first and second windings to the terminals of said printed substrate.   
     
     
       5. A magnetic detector comprising: a toroidal bobbin having a toroidal chamber defined therein, the toroidal chamber being filled with a heat insulating gel;   a ring-shaped magnetic core enclosed in said chamber and encased in said gel so as to be substantially insulated from the influences of environmental temperature; and   a coil wound about the toroidal bobbin for magnetically exciting the magnetic core.   
     
     
       6. The magnetic detector of claim 5 wherein the heat insulating gel comprises a silicon gel. 
     
     
       7. The magnetic detector of claim 6 wherein the magnetic core is composed of a permalloy. 
     
     
       8. The magnetic detector of claim 5 wherein the gel has a fluidity which substantially insulates said magnetic core from the influence of external stress.